1. Field of the Invention
The present invention relates to an engine of the type utilized to power an outboard motor, and more particularly to a fuel supply system for an engine positioned within a cowling of an outboard motor and powering a water propulsion device of the motor.
2. Description of Related Art
Fuel vapors can be problematic in the fuel-supply system for internal combustion engines, especially those of the type in which the fuel is injected with a fuel injector. Fuel vapors are unpredictable and their concentration in the fuel supply system varies. The unpredictability of the vapors causes the fuel injector to deliver fuel in a ratio to the air which may be leaner or richer than desired, resulting in poor engine performance.
Further, the fuel supply system may be used with an engine positioned in a confined space, such as the cowling of an outboard motor. In these situations, space is limited, and the fuel supply system needs to be as small and simple in arrangement as possible.
In the past, fuel-vapor separators have been provided along the fuel supply path to separate at least part of the vapor from the liquid fuel. In manifold injection systems, an electrically-operated, high-pressure pump has been positioned within the vapor separator in order to save space and to permit the pump to be cooled.
In direct injection systems, fuel is injected directly into the combustion chamber. This type of fuel injection requires that the fuel be injected at a higher pressure than with manifold injection systems, in which the injection pressure is substantially at or even below atmospheric pressure. Electric pumps are not totally capable of supplying fuel at such high pressures. Instead, a mechanical pump that is driven by the engine has been used to generate the high pressures required by direct injection systems.
In order to make the fuel distribution system more compact, the mechanical high pressure pump can be located in the vicinity of the engine's cylinder head. Similarly, the fuel rails that deliver fuel from the high pressure pump to fuel injectors can be located close to the cylinder head. Since the cylinder head is heated by lubricating oil, it becomes very hot. As heat is transferred from the cylinder head to the fuel supply system, vapors may accumulate within the fuel rails.